Bamspeedy, I note that you say my new trade system would make big civs even larger, because they tend to have more resources. That could be true, but I don't always find that to be the case when playing Civ III. But my trade system would actually also allow smaller civs to compete more easily, due to their smaller needs. Maybe I was not clear before, but my new trade system does not have one iron supplying an empire of hundreds of cities any longer...each resource gives a finite amount of itself. In Civ III, that made a source of iron more valuable to a large empire than a small one. My new trade system would force large empires to find several sources, if it wanted every city to have access to a resource, while a small empire could sell its extras to neighbors. This can actually make small civs very powerful if they, in particular, have a monopoly on a resource. They don't have to use very much of it, perhaps, but they can sell them to hungry neighbors for huge sums.
However, I do see your point in how this system may not actually decrease road use, since they provide movement bonuses as well. I agree--my trade system may not decrease road building at all. But for me, at least, it would, maybe because my strategy is just strange. I tend to expand extremely rapidly and any workers I build are sent to (near) the battlefront to facilitate transportation, or sent to build roads to cities not connected to my empire. In the process, I end up with many cities that are connected but not substantially "roaded." Personally, it is annoying to me to have to send back workers to these places to build roads just so they can generate trade. I also don't care much for movement bonuses in such areas, because they are so deep inside my empire. Maybe that is my own strange problem, but in that case my new trade system would decrease the amount of road work.
As for railroads, I think the Civ II purpose is better--shields and trade (from a resource square!) are increased by 50%, I think. Therefore, there is no point to placing railroads on every spot. To boost food, I think the Civ II concept of "farmland" is good, although I didn't like the existence of the "Supermarket" improvement.
My system certainly would make building a trade network even more important. But all (or most) players connect all their cities and resources anyway, so this will not really change much in that sense.
Then, again, I think CMcQueeny's idea of a decimal based system of calculating trade values would be a good idea--but only for those who want it (the micromanagers, I would think). Therefore, I propose that the decimals preference can be set during a the game setup, so those who don't want the additional complications can just turn it off.
But good points, everyone! Finding more to be addressed would be welcome!